1. No category

A presentation for course--
Thermal Modification of
Wood
Presented by Jieying Wang
Supervised by Dr. P. Cooper
Faculty of Forestry
University of Toronto
Objectives of Wood Thermal Treatment
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Reduce the hygroscopicity of wood;
Improve the dimensional stability of wood;
Enhance the resistance against biological attacks;
Color improvement?
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Main advantage: Environmentally friendly.
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Thermal treatment of wood is not a new technology!
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Slight charring treatment: Poles, posts and structures;
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Wood drying: Wood exposed to high temperature for some time
will have lower hygroscopicity and lower shrinkage (Tiemann 1920, 1951);
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Staybwood: Wood heat treated beneath the surface of a molten
metal, oil or fused salt, by the U.S. Forest Products Laboratory
(Tiemann 1951; Stamm and Harris 1953; Stamm 1964).
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Post heat treatment of wood-based composites;
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Decreasing growth stresses in wood (e.g. Eucalyptus);
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Plasticizing wood (usually in the presence of water);
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Fixation of compression or bending of wood;
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Accelerating reactions in wood or composites;
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Killing pests inside wood.
Long-time conditioning of wood at low temperature
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Old wood structures
ASE (anti-shrinking efficiency) of old wood can be as high as 40%.
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Species related, e.g. Teak
Rosewood low temperature drying--
1. Main Processes of Thermal Treatment
of Wood in the Industry
--Thermo Wood (or Premium wood) in Finland
--Retification Process (New Option Wood) and Le -Bois Perdure
in France
--Plato Process in Netherlands
--Oil-heat treatment in Germany (OHT-Process)
1.1 Thermo Wood (or Premium wood) in Finland
Fresh wood
Wood drying
T: 100 C, then 130 C
Time: 0-48 hrs
Heat treatment
T: 150 -- 240 C
Time: 4 hrs
Media: Steam
Cooling and
conditioning
T: 70 C
Time: 24 hrs
Developed by VTT Building Technology, Finland
(Syrj
Syrjäänen and Kangas 2000; Syrj
Syrjäänen 2001; Jä ms
msää 2001; Militz 2002a, 2002b;
Welzbacher and Rapp 2002; P. Kamdem 2002)
1.2 Retification Process (New Option Wood) and Le
Bois Perdure in France
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Retification Process (Developed by the Ecol des Mines de Saint
It treats air-dry wood (12 % m.c.)
in a specific vessel at about 240 C and in a nitrogen
atmosphere with less than 2 % of oxygen;
Etienne and commercialized by S. A.):
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Le Bois Perdure Process starts with fresh wood, applies
to the wood with a fast drying and high-temperature treatment
under steam atmosphere.
(Dirol and Guyonnet 1993;Vernois 2001; Militz 2002a, 2002b; Welzbacher and Rapp 2002;
Jermannaud et al. 2002 ; P. Kamdem 2002)
1.3 Plato Process in Netherlands
Green or
air-dry wood
Hydrothermolysis
T: 160-190 C
Time: 3-5 days
Pressure
Dry curing
T: 170-190 C
Time: 14-16 hrs
Conditioning
Time: 2-3 days
(MC: 10 %)
(Tjeerdsma et al. 1998a, 1998b, 2000; Militz and Tjeerdsma 2001; Boonstra et al. 1998; Militz
2002a, 2002b; Welzbacher and Rapp 2002 ; P. Kamdem 2002)
1.4 Oil-heat treatment in Germany (OHT-Process)
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It is carried out in a closed
vessel, with hot crude vegetable
oil circulating around the wood
during the treatment, usually at
the temperature of 200-220 C.
(Sailor et al. 2000a, 2000b; Rapp and Sailer
2001; Militz 2002a, 2002b; Welzbacher and
Rapp 2002 ; P. Kamdem 2002)
(from Rapp and Sailer 2001)
Table 1. Comparison among the five wood heat treatment processes
Media
Wood initial M.C.
Treatment
Temperature( C)
Steps
Approximate
Cost (Euro/m 3)
Oil-heat
treatment
(Germany)
Hot oil
Air-dry, e.g., 6%
180~220
One step
Thermo Wood
(Finland)
Steam
Fresh wood
150~240
Temperature rising and
drying, heat treatment, and
cooling and condtioning
Retification
process
N2
Air-dry, e.g., 12%
200~240
One step
150~160
Bois Pserdure
Steam
Fresh wood
200~240
One step
100
Plato process
(Netherlands)
Steam
or air
Green or air-dry
wood
170~190
Hydrothermolysis, drying,
and curing
100
65~95
1.5 Applications of thermally Treated Wood
Above ground non-structural use:
Siding, cladding;
Decking and flooring;
Garden furniture;
Children playground;
Window and doors frame;
Indoor furniture;
Musical instrument.
(From P. Kamdem. 2002)
(From P. Kamdem. 2002)
(From P. Kamdem. 2002)
(From P. Kamdem. 2002)
2. Properties of Thermally Treated
Wood
----Durability: Biological durability, weathering, reological
properties
----Hygroscopicity, dimensional stability and water absorption
----Mechanical properties
2.1 Biological Durability
--Against microorganisms: bacteria, fungi (blue stain,
white rot, brown rot, soft rot)
--Against insects: e.g. beetles, termites
--Against marine borers: e.g. shipworms
Biological durability of treated wood
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Staybwood: Considerable decay resistance (Stamm and Harris 1953; Stamm 1964);
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Thermo Wood: Improved biological resistance at higher than 220 C and
longer than 3 hrs, no increasing durability in ground contact (Jämsä and
Viitaniemi 2001);
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Retification process: Temperatures of 230~240 C are ideal for the durability
(Vernois 2001);
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Plato process: Improved durability against decay fungi and soft rot fungi,
especially against brown rot fungi. And the hydrothermolysis has more
effects on soft rot and brown rot decay, while the curing step has more
effects on white rot decay (Tjeerdsma et al. 2000, 1998b; Militz and Tjeerdsma 2001);
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Oil-heat treatment: At the highest temperature of 220 C, the wood gains the
highest resistance against fungi, especially to brown rot fungi, but no
improved durability against marine borers (Rapp and Sailer 2001; Sailor et al. 2000a,
2000b).
Durability classification of treated wood
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The Plato wood and the oil-heat treated wood can be classified as “durable”,
the Thermo wood and the Retified wood can be classified as “moderately
durable” (according to EN 350-1), but there are only slight differences in
the mass loss during decay tests among the four processes (Welzbacher et al.
2002);
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The heat treatment of the French process could improve the durability of
wood from non-resistant to moderate or resistant species depending on the
fungi (ASTM 2017), but the treated wood was not sufficiently decay
resistant to ground contact use without further protection (Kamdem et al. 1999,
2002).
Special reports----
Resistance of oil heat treated wood to Formosan
Subterranean Termites (by W. R. Smith et al. 2003)
Scots Pine
Norway Spruce
Heat treatment
Media: rape seed oil
T: 220 C
Time: 4 hrs
Conditioning
T: 120 C hot air
Time: 24 hrs
Vacuum pressure
Impregnation
T: 120 C
15 mins V at 20 mbar,
15 mins P at 10 bar
Conditioning
T: 120 C hot air
Time: 24 hrs
Retention: 0.40 gm/cc
(Sample preparation was done by Bundesforschungsanstalt fur Forst- und Holzwirtschaft
and provided to the Louisiana Forest Products Laboratory)
Hot oil treatment schedule
Average density change before and after treatment
SPHT: Scots pine heat
treatment
SPHTI: Scots pine heat
treatment and impregnation
NSHT: Norway spruce heat
treatment
Results of sample weight loss and termite mortality after 28 days
no choice laboratory test
SPC: Scots pine control
SPHT: Scots pine heat
treatment
SPHTI: Scots pine heat
treatment and impregnation
NSC: Norway spruce
control
NSHT: Norway spruce heat
treatment
SYPC: Southern yellow
pine control
Main results of this study
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Only heat treatment in hot oil was not effective to
resist Formosan subterranean termite.
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Scots pine with a combination of hot oil treatment
then vacuum pressure treatment with hot oil was
found to show promise in increasing resistance to
FST attack (28 days, AWPA E1-97).
Formosan subterranean termite
2.2 Weathering resistance
--Against UV: color change, wood degradation (especially lignin) and surface
roughness;
--Against moisture fluctuation: swelling, crack;
--Against temperature fluctuation and other outdoor conditions
Special reports----
Weathering of ThermoWood
(by S. Jämsä et al, 2000)
Heat treament
T: 225 C
Time: 6 hrs
Planed or sawn
spruce and pine
(WL higher than 10%)
Coated with commercial
coatings for exterior cladding,
window joinery or fences
CCA treated
as reference
Weathering vertically
on the racks in Espoo,
in Finland
Weathering assessment
(Color, roughness, crack,
flake of coating, MC of wood)
Weathering of uncoated heat treated wood----
Moisture change----
Moisture change ----
Performance of the coating----
Conclusion of this study
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Without coating the heat-treated wood is not weather resistant. The original
dark brown color turns grey.
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Cracking of the heat-treated wood without coating was at the same level as
that of the untreated wood despite the lower moisture content of the heattreated wood. The unpigmented or low build stains and oils did not prevent
cracking of the heat-treated wood.
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Weather resistance of the heat-treated wood was improved by the water- or
solvent-borne paints. Heat treated wood as a substrate for coatings is
comparable to untreated wood .
2.3 Hygroscopicity, Dimensional
Stability and Absorption
--Hygroscopicity : i.e. Adsorption of wood;
--Dimensional stability: ASE (important index);
--Water absorption: Related to porosity of wood
Anti-swelling efficiency (ASE)
S: Swelling;
Dw: Wet dimension, after immersion in water or
conditioned at high humidity;
Dd: Dry dimension, after ovendrying.
ASE: Anti-swelling efficiency;
Snt: Swelling of non-treated sample;
St: Swelling of treated sample.
Results of Staybwood-Heating at 320ºC for 1
min or at 150ºC for 1 week,
ASE: 40% to 50%;
The temperature decreases
linearly with the increase of
the logarithm of the time for
a given ASE;
The ASE increase seems
to be associated with the
darkening of wood.
T (ºC)
(Stamm and Harris 1953; Stamm 1964)
Results from Europe-p
Thermo Wood: Wood gains the swelling reduction of about 80% to
90%, while its equilibrium moisture content (EMC) is reduced by 40% to
60% (Syrjänen and Kangas 2000);
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Retification Process (New Option Wood): Heating in nitrogen at
the temperatures of 180 C to 220 C, EMC of wood is 4-5%, instead of 1012% (Vernois 2001), and the corresponding dimensional stability of wood is
improved by about 50% (Jermannaud et al. 2002);
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Plato Process: Wood can obtain the swelling (or shrinking) reduction
about 50%, generally with the higher reduction in the tangential direction
than in the radial direction (Tjeerdsma et al. 1998b; Militz 2002a, 2002b);
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Oil-heat treatment: At 220 C for 4 hrs, wood has the fibre saturation
point of 14%, compared with 29%
(Rapp and Sailer 2001).
Hygroscopicity results from D. P. Kamdem et al. (2002)-Heat treatment: Retification Process in France, Maritime pine, spruce, beech and
poplar, dimensions of 5 cm*10 cm *200 cm, at 200-260ºC for 1-24 hrs.
The reduction of hygroscopicity seems more obvious
for hardwoods and at higher humidities.
Swelling results from D. P. Kamdem et al. (2002)--
The swelling in water is reduced, but the swelling in NaOH?
Swelling reduction of Eucalyptus
(Santos 2000)
Water absorption
Water adsorption
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The thermally treated wood may
have higher water absorption (Vernois
2001), larger pore sizes and broadened
pore size distribution, and higher
diffusion coefficient of water along
the tracheid axis (Hietala et al. 2002).
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Oil heat treated wood?
Microstructure of Pine: Cell
lumena and also pores in cell walls
2.4 Mechanical Properties
--Toughness
--Abrasion resistance
--MOR (modulus of rupture)
--Hardness
--MOE (modulus of elasticity)
--Screw and nail withdrawl load
Effect of heat on mechanical properties
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Youngs (1957): Most of the mechanical properties or rheological
properties of wood in the transverse direction are significantly affected by
the heat treatment at 82 C for 30 days;
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Shafizadeh and Chin (1977): Wood may lose 10% of its original
MOE heated at 120 C for about one month.
Mild heat treatments at temperatures ranging from 140 C to
200 C within certain time limit increase the MOR and MOE of
wood (Dwianto 1999a; Santos 2000).
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The biggest disadvantage—Great reduction of
mechanical properties!
The reduction of the mechanical properties depends on the
temperature, time, heating media of the heat treatments, the
species and so on:
Drastic reduction of the mechanical properties of wood, especially the toughness,
abrasion resistance and MOR. For the hardness, a reduction of 21% at ASE of 40%
and a reduction of 33% at ASE of 60% for wood heat-treated in the absence of air
were reported (Stamm and Harris 1953; Mitchell 1988);
Retification process: Heat treatments may decrease the MOR of wood by 30% to
40% at 230 C (Vernois 2001);
Oil heat treatment: At 220 C, the MOR is about 70% of those of the untreated
samples, while the MOE does not drop greatly. The impact bending strength is only
about 51% of the value of the controls (Rapp and Sailer 2001; Sailor et al. 2000b).
Bending results from D. P. Kamdem et al. (2002)--
The bending performance of Beech was more severely attacked!
2.5 Other changes after heat treatment of wood
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Color darkening;
Weight loss and density decrease (YILDIZ et al. 2003);
Smell. However, the emission factor of Thermo Wood, expressed as TVOC and
as specific compounds, was less than that of the untreated reference (Bengtsson et al.
2003);
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Spotted discolorations of rosins (Jamsa and Viitaniemi 2001);
Disappearance of rosins on the oil-heat treated wood (Rapp and Sailer 2001) and
remove of blue stain in Retification Process?
Coating characteristics: For Thermo Wood, adhesive performed very well
whereas PVAc adhesive showed an unacceptable percentage of delamination
(Bengtsson et al. 2003).
3. Chemical Changes of Wood during
Thermal Treatment
--Changes of extractives in wood?
--Changes of hemicellulose
--Changes of cellulose
--Changes of lignin
Cell wall structure of wood
ML: Middle lamella
P: Primary wall
S1: Outer layer of secondary wall
S2: Middle layer of secondary wall
S3: Inner layer of secondary wall
http://www.extension.umn.edu/distributi
on/naturalresources/images/6413f1-7.gif
General heat stability of wood components
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Wood begins to degrade obviously at the temperature of about
165 C (Stamm and Hansen 1937).
Heat Stable?
Hemicellulose
225 ~ 325 C
Decomposition
temperature
Cellulose
Lignin
325 ~ 375 C
250 ~ 500 C
(Shafizadeh and Chin 1977)
180 ~ 300 C
240 ~ 400 C
280 ~ 550 C
(Kuriyama 1967)
Traditional explanations of chemical changes
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Ether linkages? But the swelling of the treated wood in sodium hydroxide,
pyridine, or morpholine was still high, instead of the reduced swelling as in the
case of formaldehyde crosslinked wood (Stamm and Hansen 1937; Seborg et al. 1953; Stamm
and Harris 1953; Stamm 1964);
p
The improved dimensional stability and decay resistance are attributed to the
formation of cross linking and esterification reactions during the heat
treatment (P. Kemdem 2002);
p
The formation of furfural, a less hygroscopic substance from hemicellulose
(Stamm and Hansen 1937; Seborg et al. 1953; Stamm and Harris 1953; Stamm 1964) and also from
cellulose;
p
But furfural is unstable in the reaction mixtures and its amount is not high
enough to be so critical for the wood properties (Bourgois et al. 1988).
Explanation from Plato Process
Hemicellulose
Hydrothermolysis:
Hemicellulose
Cellulose
Formaldehyde
Furfural
Water
Acetic acid
Lignin
Degrade
Autocondense
Curing step:
Lignin
CH2
Lignin
Esterification and other reactions
(Tjeerdsma et al. 1998a; Militz and Tjeerdsma 2001)
Chemical changes of hemicellulose--
and amorphous and
short-chain polymer!
http://natural-resources.ncsu.edu:8100/wps/k12activities/ppts/forest/img043.gif
Chemical changes of hemicellulose
p
Generally, hemicellulose (more pentoses) of hardwoods is more unstable than
that of softwoods (more hexoses ) (Kamdem et al. 1999, 2002; Bourgois et al. 1988);
p
Much of the acetic acid (and water?) should be attributed to the
decomposition of hemicellulose, especially to hemicellulose with acetyl
groups, and hardwoods have higher acetyl groups than softwoods (Browne 1958;
Bourgois et al. 1988; Sivonen et al. 2002);
p
Thermo Wood: The destruction and deacetylation of hemicelluloses is one of
the most remarkable changes of thermally treated wood revealed by solid
state NMR (Sivonen et al. 2002).
p
Heat decomposition of beech with restricted air supply: Pentosan content
decreases by 8% at 171 C and decreases by up to 20% at 206 C. At 245275 C, 45% of the pentosan and 40% of the acetyl groups are decomposed or
separated (Sandermann and Augustin 1964).
Side proofs for hemicellulose decomposition
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After slight pyrolysis: the hydrogen and oxygen decrease, while the carbon
ratio increases greatly (Bourgois et al. 1988; Dirol and Guyonnet 1993);
p
The treated wood shows a rapid drop of the hydrophilicity from the
beginning of torrefication (Bourgois et al. 1988);
p
Heat treatment of paper causes less strength loss (less darkening?) due to
less hemicellulose present in paper (Stamm 1964);
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The loss of hemicellulose during incipient brown rot decay of southern
pine leads to high levels of strength loss, and the significant loss of glucan
(representing cellulose) was barely detected until more than 75% of the
original MOR was lost, and the MOR loss appeared to occur at a greater
rate than the MOE loss (Curling, 2001).
Conclusion for hemicellulose decomposition
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It seems reasonable that the increase of dimensional stability and biological
resistance, and the reduction of mechanical properties during heat
treatments are mainly attributed to the breakdown of hemicellulose;
p
The degradation products from hemicellulose are not confined to furfural
only, and there could be some cross-linking and polymerization reactions
associated with hemicellulose taking place during heat treatments of wood.
Chemical changes of cellulose--
With high polymerization
and crystallinity degree.
http://natural-resources.ncsu.edu:8100/wps/k12activities/ppts/forest/img039.gif
Changes of cellulose
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p
p
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Sandermann and Augustin 1964: During heat pyrolysis of cellulose, only
insignificant decomposition takes place before 257 C and its IR and X-ray
spectra remain unchanged, though the numbers of carboxyl and carbonyl
groups increase a little;
Bourgois et al. 1988: Cellulose does not undergo noticeable modifications
in its crystallinity during torrefication of wood sawdust at 260 C by
studying its X-ray spectra.
Sivonen et al. 2002: The most remarkable changes revealed by solid state
NMR were the increase in relative crystallinity of cellulose.
Brown 1958: Some of the carbon-to-oxygen bonds in the links between
glucosan units of cellulose might cleave along the chains early in the
pyrolysis, especially in the presence of water and some acids, and
levoglucosan was the characteristic product of the primary pyrolysis of
cellulose.
Chemical changes of lignin--
Structure of lignin
Methoxyl
Softwood: Guiaicyl
Hardwood: Syringyl
Ether
Methylene
From http://helios.bto.ed.ac.uk/bto/microbes/lignin.jpg
Changes of lignin
p
During heat treatments, the lignin content and the carbon content in wood
increase (Bourgois et al. 1988; Dirol and Guyonnet 1993), especially for hardwoods
with higher contents of hemicellulose (Kamdem et al. 1999, 2002).
p
After torrefication of sawdust at 260 C for 4 hrs, lignin increases from 28%
to 84%, analysed by sulphuric acid method (Bourgois et al. 1988).
p
The ether linkages in lignin are easier to cleave during pyrolysis (Browne
1958). From 200ºC to 250ºC, carbon dioxide and other compounds are
liberated from lignin; from 250ºC to 400ºC, phenolic and neutral oils etc.
are produced, some of them tend to polymerize, and the heat decomposition
of lignin becomes exothermic at about 270ºC (Stamm and Harris 1953, p. 66).
p
Changes in the lignin fraction were mostly registered as diminishment in
the methoxyl content (Sivonen et al. 2002).
Condensation of lignin
p
Funaoka et al. (1990) found that during heat treatments of wood at the temperatures
from 120 C to 220 C, lignin mainly undergoes the diphenylmethane type of
condensation, especially in the presence of moisture in wood.
p
Lignin seems to be the most reactive among wood components in auto-crosslinking
reactions (Back 1967; Back 1987);
p
Thermo Wood: Demethoxylation of lignin and stable free radicals are observed and
it is believed that the radicals take part in condensation reactions leading to
crosslinks within lignin and possibly with other components present (Sivonen et al.
2002).
Conclusion of lignin changes
p
There are some cleavage reactions in the weak points of lignin, and there
are also some condensation reactions associated with lignin and also with
some breakdown products from the main components of wood cell walls.
Lignin and acid number changes results from D. P. Kamdem et
al. 2002
The increase of lignin means the decomposition of hemicellulose even a little cellulose
during the treatment, especially for beech with more pentoses than hexoses.
The acid numbers indicates the carboxylic groups or those which are highly susceptible to
converting into carboxylic groups in wood, which are reduced during the heat treatment.
4. Effects of External Factors on Thermal
Treatment of Wood
--Oxygen
--Moisture
--Inorganic chemicals
--Various heating media
4.1 Effect of oxygen—Oxidation?
p
Most of the heat treatments are carried out in the absence of oxygen, for
biological resistance and mechanical properties of wood?
p
Presence of air during heat treatments leads to higher ASE, higher weight
loss, and oxygen acts like a catalyst for the changes of wood components
during heating (Dwianto et al. 1997; Wang et al. 2000a);
p
Mitchell (1988) found that the effects of oxygen on thermal degradation of
wood depended on the MC of wood, with greater effects on oven-dry
specimens, and oxygen had more influence on MOR and MOE than on
reflectivity of wood surfaces.
Comparison of ASE of heat treated fir in air or in relative vacuum
ASE (%)
Treatment time (hr)
Comparison of WL of heat treated fir in air or in relative
vacuum
WL (%)
Treatment time (hr)
4.2 Effect of moisture—Hydrolysis of wood and degradation of
heating media?
p
The existence of water in wood during heating must speed up the heat
transfer, and accelerate the decomposition of the main components of wood
cell walls, since hydrolysis is one of the easiest reactions for wood
carbohydrates;
p
Skaar reported that the heat degradation was 10 times faster for wet wood
than for dry wood (reviewed in Yildiz 2002);
p
Burmester (1973) found that certain moisture in wood led to higher ASE
and little reduced strength of wood under certain pressure, and the optimum
MC of wood for the heat treatments ranged from 20% to 30%;
p
During kiln drying of wood, high humidity in the environment reduces the
hygroscopicity of wood more than the low humidity does, while higher
temperature is needed to achieve the similar reduced hygroscopicity in the
case of dry wood (Hillis 1984).
4.3 Effect of inorganic chemicals
Inorganic chemicals: e.g. phosphoric acid (H3PO4), diammonium phosphate
((NH4)2HPO4), diphenyl phosphate and zinc chloride (ZnCl2);
Main function: Producing more charcoal, accelerating heat transfer?
(Browne 1958; Shafizadeh and Chin 1977;
1977 Fung 1974, 1976; Stamm and Hansen 1937; Levan
Levan))
Flammable gases
levoglucosan
Wood
Cellulose
Hemicellulose
Lignin
Tar
levoglucosenone
Char
Effect of inorganic chemicals on pyrolysis of wood
4.4 Effect of different heating media
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p
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Air
Steam
Nitrogen and other inert gases
Molten metals
Relative vacuum
Other mineral or vegetable oils?
Vegetable oils
p
All vegetable oil and animal fats consist
primarily of triglyceride molecules as shown
schematically below. R1, R2, and R3
represent the hydrocarbon chain of the fatty
acid elements of the triglyceride.
p
The properties of the triglyceride will be
determined by each fatty acid. Fatty acids are
designated by two numbers: the first number
denotes the total number of carbon atoms in
the fatty acid and the second is the number of
double bonds. For example, 18:1 designates
oleic acid which has 18 carbon atoms and one
double bond.
http://www.me.iastate.edu/biodiesel/Pages/bio2.html
--Composition of various oils and fats
Myristic
Palmitic
Stearic
Oleic
Linoleic
Linolenic
Arachidic
Gadoleic
14:0
16:0
18:0
18:1
18:2
18:3
20:0
20:1
Soybean
6-10
2-5
20-30
50-60
5-11
Canola
3.9
1.9
64.1
18.7
9.2
0.6
1.0
Hi erucic
rapeseed
3.0
0.8
13.1
14.1
9.7
7.4
50.7
44.1
4.4
39.0
10.6
0.3
0.2
3-4
0-1
4-15
Oil or fat
Palm
1.1
Tung oil
75-90
Lard
1-2
28-30
12-18
40-50
7-13
Tallow
3-6
24-32
20-25
37-43
2-3
0-1
--Oxidative Stability of Oils and Fats
Rating
Worst
Best
Fat or oil
Inherent oxidative
stability
Total double bonds
Calculated iodine
value
Safflower
9.546
168.8
146.1
Soybean
8.579
153.7
133.1
Sunflower
8.489
156.3
135.3
Corn
7.708
148.4
128.4
Cottonseed
6.895
130.1
112.6
Canola
5.349
131.3
113.3
Peanut
4.326
112.6
97.1
Lard
2.426
68.5
59.3
Olive
1.74
95.6
82.4
Palm
1.724
60.8
81.8
Tallow
1.267
55.6
48.4
Palm kernel
0.430
20.1
17.2
Coconut
0.360
11.1
9.6
--Approximate prices of oils and fats
Oil or fat
Price in 1997 (US $/ ton)
Average price during 19921997 (US $/ ton)
Tallow
457
392
Soybean
513
528
Sunflower
517
580
Corn
547
555
Fish oil
548
427
Rapeseed
565
563
Lard
575
561
Cottonseed
584
564
Palm
601
580
Linseed
799
747
Coconut
899
758
Castor
915
899
Palm kernel
915
899
Peanut
990
951
Safflower
1301
1344
Tung
2238
1560
Future research on wood thermal treatment
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To develop the applications for such a modified wood material;
To optimize the industrial processes and the various parameters;
To find some new wood heat treatment processes;
To try some combined wood modifications;
To clarify the chemical changes of wood during the thermal treatment.
Main References
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